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That's kinda what I was thinking. After the DME went bad back in November, l intended to test a few things like that when I got the new one for future reference. Of course, regrettably, I didn't.
If the DME just sees the reference sensor and then sends that information directly to the tach independent of fuel/spark, that means it has to be in the sensors or DME. I may try sraight wiring the sensors to the DME.
You ever notice how 951 issues tend to come in waves.....kinda like the flue. And both make you sick. When someone posts a problem, we all get the same problem....makes you go hmmmm?
On to my flue bug....
Last week drove my car from Las Vegas to California. Twisties, high speed, razor sharp adrenaline....and my 951 ran as good or better than it ever has. Parked it, put the car cover blanky on and gave it a loving pat. Love my car. Four days later, uncover my beauty, turn the key in anticipation of another glorious run.......no start. Hate my car.
No spark, no injector pulse, no tach bounce. Order (2) new speed/reference sensors from my favorite Porsche parts counter (learned long ago that trying to save a penny on after market parts WILL cause you grief). Happen onto this post, great read......flue bug spreading, hmmmmm? Get shiny new sensors in (3) days, remove old sensors.....surprise, sensor connectors are crispy.
Notice new connector vs old sensor connector.
Plug in new sensors....and still no start, no tach bounce. Remove connectors, maybe I reversed the two sensors (not a chance, I am very cautious)? When low an behold what do I find....I have a super, penicillin resistant virus. The DME side of the connector wire has been fried! And of course, the wire fried on the side of the wire facing down so that it was hidden......never easy. Now it’s on repairing the wire.....and cross my fingers the virus has passed to another unsuspecting victim.
Appreciate the offer Tom! I still work in the Bay Area during the week, and have the S2 cab here as well. I was wondering if these wires were shielded and thus not repairable. Thanks to your response, looks like I will be ordering a new harness. Not looking forward to snaking in a new one, it runs in some pretty tight spots.
You were right, Lindsey Racing. Ordered. Much appreciated Tom!
When you get the LR harness before install just make sure the pins on the harness are seated in the connector. I had back in 2010 one of the pin locks unseated in the new harness. Just had to push on the wire to get it to lock. Fixed my no start issue when I did my build. LR has a new harness manufacturer now. Still a great product was just something minor that I may have done or the tech that built it didn't seat it to begin with.
Well, I finally got around to working on the car this weekend. It still won't start, but I learned a couple of things and I have a clearer picture of what is working. First a note on something I stumbled across while perusing the Internet. Just as a reminder, my car is a non-turbo. What I discovered is that for as long as I have had the car, I have been running a turbo spacer (figure 8 washer) under the speed sensor. When I first built the car, I guess I ordered the wrong part. What's interesting is that the car ran fine with this 2.0 mm spacer. Apparently, the NAs have either a 0.3 mm spacer or no spacer at all. When I got the car, it had no spacer, but I thought it needed one. Anyway, I have now removed the spacer. It didn't help with the starting, but boy did i get excited when I discovered this. I just knew this was the problem, but apparently not.
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So, here are the results of some tests I ran this morning. I switched between the Bosch and the Facet sensors as I would like to return the Bosch sensors since they didn't fix the problem.
I tested the terminals using a backprobe. This is a nice technique as it allows the connector to be plugged into the DME while testing. Here's what that looks like:
First I tested terminals 25 & 26 at the DME connector. Here are the results:
As you can see, it looks pretty good. I'm getting +4-4.5 volts above 0. Spec is greater than 2.0 volts. Next I tested terminals 8 and 27 at the DME connector:
Again, the results look pretty good. I'm getting about 5+ volts +peak to -peak. Spec is greater than 2.5 volts peak to peak. Next I took a look at terminal one and ground:
As you can see, when I turn the key, the volts on terminal one jump to 12 volts. This is to be expected. Unfortunately, terminal one does not ground which is what fires the coil. Just for reference, I ran a two channel test with channel A being terminal one and ground and B being terminals 25 and 26:
As you can see, the reference signal looks good, and I have 10 volts or so on terminal one, but it never grounds. BTW, I ran this test with a spark plug in the coil wire grounded in the engine compartment so that I could eliminate the distributor, etc. I also verified that I have 12 volts on the positive side of the coil. Just to round things out, I ran the same test with the speed sensor:
So at this point, I am pretty frustrated. I think the only thing it could be is a bad DME. But, I already sent the DME back to ECU Doctors and they said it checked out fine. I would really like to be able to test the car with a known good one though.
Does anyone have any ideas for things I can check? What could I possibly be missing here?
Joe, what year is your 944 and does it have an alarm module where the DME is located?
If you have an alarm, it can prevent fuel and spark.There is a way to bypass it, but the jumpers are slightly different between model years.
Thanks all. It's an '87. No alarm as far as I can tell. Certainly not the factory version with the key to the rear of the driver's door. And yes, non-turbo, so no KLR.
If anyone is in the north Atlanta area and has known working DME for an '87 944 I could borrow for a few minutes, I would certainly appreciate it. I could make it worth your while.
06-24-2018, 07:53 PM
